Evidence is accumulating that enterotoxin elaborated by certain strains of Escherichia coli may be an important determinant in acute diarrheal disease. It is now clear that this enterotoxin has a heat- labile (LT) and a heat-stable (ST) component that are considerably different in chemical structure, immunologic response and even in mechanism of action. We propose to develop improved assay methods for demonstrating these toxins and their immunologic response in appropriate animal models. These studies will be facilitated by purification of the enterotoxins. We have preliminary evidence that purification may be feasible by using agents active on bacterial cell membranes. Another area of study is the genetic mechanisms within toxigenic E. coli that $ direct LT and ST production. Specific plasmics have been identified that can be tranferred into appropriate recipient E. coli cells with the genetic information to initiate enterotoxin production.